In many situations, devices must operate in potentially hazardous conditions, such as where a fuel mixture may be ignited by uncontrolled operating or environmental conditions. For example, vehicles, including aerospace vehicles, typically operate with a fuel that must be maintained in a safe condition during storage and use. The ignition hazard should be minimized even when the vehicle is subject to uncontrolled events such as an accident, electrical malfunction, a lightning strike, or static electrical discharge. Other applications requiring ignition hazard consideration include fuel transport, fuel storage, mining operations, and operations which involve combustible particulate such as sawdust, flour, and grain.
In the aerospace industry, lightning strikes of aircraft are a concern because they could result in electrical arcs and/or heating sufficient to ignite vaporous fuel mixtures. Though lightning passes through metallic aircraft virtually always without resulting harm, manufacturers and regulators are vigilant to the potential for harm. The Federal Aviation Authority (FAA) recognizes that arc energies as low as 200 μJ (microjoules) may be sufficient to cause unwanted ignition of vaporous fuels.
Design of apparatuses exposed to ignition hazards typically involves reducing the likelihood of ignition, containing the ignition hazard, and/or withstanding the ignition hazard. Test systems may facilitate the design by simulating ignition of a combustible fluid in a controlled environment. To initiate ignition of a combustible fluid, test systems may include an arc source, i.e., a source of electric discharge, sometimes referred to as a spark. This discharge may be used to ignite a combustible and/or explosive material (typically gaseous or vaporous), in particular to test a test sample, such as combustible and/or explosive materials (including fuel mixtures), and structures, devices, and/or apparatuses intended to operate near ignition hazards. The arc source may be used to simulate unwanted electrical discharge, to verify that test conditions are proper for ignition, and/or to calibrate the ignition point for a combustible and/or explosive material.